Directed energy technology is being developed for a broad range of applications including both lethal and non-lethal weapons, burst communications, and explosion diagnostics. These systems use a pulse power generator to provide a burst of energy to an energy projection system such as a laser, a radio frequency (RF) antenna, or a microwave frequency (MW) antenna. A variety of generators have been developed for single shot systems. One type, known as a ferroelectric generator (FEG), uses conventional explosives to launch a shock wave into a piece of polarized ferroelectric ceramic. The shock wave causes the ceramic to depolarize, liberating a large amount of charge that is then available to do work such as drive an RF or MW antenna. FEGs are compact, inexpensive power sources that are particularly attractive for highly space-constrained applications.
The current state-of-the-art FEG material is a piezoelectric ceramic based on Type I PZT-Pb(Zr0.52,Ti0.48)O3. This material is a polycrystalline aggregate that does not completely depolarize during shock, or in other words, the fractional amount of depolarization α that occurs during shock is less than 1. Most often, this material has a moderate remnant polarization Pr of about 20 to 25 μC/cm2 (C=coulombs), and a dielectric constant ∈r greater than about 1000. Most Type I PZT-Pb(Zr0.52,Ti0.48)O3 materials have dielectric breakdown strengths ranging from 30 to 100 kV/cm.
Another FEG material is Pb(Zr0.95,Ti0.05)O3 ceramic, otherwise known as 95/5 PZT ceramic. This material is not generally available commercially. Like the Type I PZT-Pb(Zr0.52,Ti0.48)O3 material, 95/5 PZT ceramic is a polycrystalline aggregate of randomly oriented, micrometer-sized crystallites. This material undergoes a phase transition from a polarized ferroelectric state to a non-polarized anti-ferroelectric state during sufficiently strong shock events. This causes complete, instantaneous depolarization, so that the fractional amount of depolarization approaches α=1. Also, when this material is doped with a small amount of Nb5+ in place of Zr4+ and Ti4+, the material has a high Pr in the range of 39 to 40 μC/cm2. This material also has a lower dielectric constant ∈r in the range of 300 to 400. Similar to the Type I PZT-Pb(Zr0.52,Ti0.48)O3 materials, this material also has breakdown strengths ranging from 30 to 100 kV/cm.
What is needed to improve FEG performance is a ferroelectric material with improved processing qualities such as resistance to thermal shock, decreased lead volatility, and improved density.